It has been know since the 1700s that nerves carry their signals throughout the body by electricity. Far more recently, we have learned that we can partially control those signals by applying an electrical signal to a nerve ending. One of the most difficult forms of nerve stimulation is the creation of artificial sight by electrically stimulating the retina.
U.S. Pat. No. 5,109,844 (“De Juan”) and U.S. Pat. No. 5,935,155 (“Humuyan”) disclose systems for the electrical stimulation of the retina by a retinal electrode array held against the retina. Retinal Tacks, first used to repair detached retinas, provide one method of attaching a retinal electrode array such as those described in De Juan and Humuyan. U.S. Pat. No. 6,165,192 (“Greenberg”) describes retinal tacks and methods of implanting retinal tacks to secure a retinal electrode array.
Some prior retinal tacks pierce the retina and sclera, and attach via an integral barb to the back side of the sclera. The problem with the prior art, is that scleras vary in thickness. If a tack is too long for a given sclera, the retinal electrode array will not be held in contact with the retina, causing poor electrical contact with the retina. If the tack is too short, the retinal electrode array will apply too much force on the retina, limiting blood flow under the retinal electrode array. This limited blood flow causes a condition similar to glaucoma. The effects of glaucoma begin when the vitreous humor reaches a pressure of 0.2 g/mm2. Therefore the pressure exerted by the retinal electrode array must be less than 0.2 g/mm2.
Medical tacks have been used in other applications, such as reattaching a detached retina and repairing a torn eardrum. Again, the tissue behind the eardrum can vary in thickness, causing too much or too little force on the damaged eardrum when a tack is inserted. A system is needed which is capable of holding a medical device in contact with tissue, or holding two pieces of tissue together, without exerting such force on that tissue, that the tissue is damaged.